Floating offshore installation for the oil and gas exploration, development of oil and gas fields and exploration of oil and gas, are kept in position by means of anchors. The anchors are placed at the sea bed, moved and taken up by means of supply ships and anchor handling ships.
The anchors are lifted and lowered by means of wires operated by winches at the deck level of the supply or anchor handling ship. The wire used to lift an anchor is normally operated by a winch placed close to the forward end of the cargo deck. The wire runs over the deck and over a redirecting body or roller at the rear end of the cargo deck. One of the critical operations in anchor handling are bringing the anchor from the sea on board the ship, and bringing the anchor from the ship's deck out in the sea, respectively. During this phase the anchor, the wire and the winch are exposed for greater forces than during other parts of the operation.
The result of this imbalance is that the wire has to be dimensioned for the force that is necessary during the above mentioned critical operations. Additionally, there is a danger for the wire to break. A wire that breaks during this kind of stress represents a great danger for the ship, equipment and personnel. Additionally, the anchor could cause severe damage to subsea installations below the ship.
NO 2004 1314 describes a ramp for handling of rig anchors on a supply ship. The ramp has two rollers, a lower roller and an upper roller, where the ramp may be pivotally rotated about the axis of the lower roller between an upper position where the ramp has an angle relative to the horizontal plane of about 60°, and a lower position having an angle of about 30°. Even though the forces caused by the anchor during the above mentioned phase is substantially reduced, compared with the old method, the forces are still high and the safety risks caused by the high forces are still present.
WO2006/073316 relates to a safe anchor handling device and methods for putting an anchor out into the sea from the deck of a vessel, and taking an anchor onboard a deck of a vessel, respectively. The device comprises a ram having a resting surface for an anchor, where the rain is displaceable from an inboard position where the resting surface is substantially horizontal, and an outboard position where the resting surface is substantially vertical. This ramp avoids the problem mentioned above related to bringing the anchor from the sea and onto the deck and bringing the anchor from the deck an out into the sea. The ramp has, however, not been a success and has only been installed onboard one vessel. The main problems are that the ramp in its vertical position is regarded to constitute a safety risk in that it blocks the astern view the deck and bridge and thus the visual control with the operation, and that that the buoyancy at the aft part ov the vessel is substantially reduced. Additionally, the effective area of the cargo deck is reduced, a reduction that is negative for the use of the vessel for other purposes.
Additionally, the device according to WO2006/073316 has a relatively complex and heavy construction. Accordingly, there is also a need for a simplified and lighter solution.
Accordingly there is a need for a method and a device for avoiding the problems described above connected to the operations of taking the anchor onboard a ship and bringing the anchor from the deck of a ship out into the sea.
An object of the present invention is thus to provide an anchor handling device that overcomes the problems described above.